1. Field of the Invention
The invention relates to an elevating platform, and to a method of controlling such a platform.
2. Brief Description of the Related Art
It is known that the operation of an elevating platform can be made more reliable by determining limit values for certain operating parameters for such an elevating platform. It is known from FR-A-2 908 119 that it is possible to define a volume defined by a “safety nomogram” within which the top end of the boom of an elevating platform must be maintained, in order to prevent the elevating platform from tipping. As mentioned in EP-A-1 378 483, the stability envelope for an elevating platform is defined on the basis of the physical characteristics of said elevating platform, such as the length of the boom or the weight of certain portions of the machine. When the machine has an inclinable boom, the safety envelope relates mainly to the relationship between the maximum height that can be reached by the end of the boom and the offset of said end of the boom relative to a central axis of the chassis of the elevating platform. The operating conditions of an elevating platform also include limit values resulting from its environment, in particular from the speed of the wind to which it can be subjected, the slope or cant of the ground on which it is resting, or the weight of the load that it can bear.
The elevator means for elevating the platform are generally controlled by an electronic unit that takes account of those various parameters and limits the movements of the elevating platform when said elevating platform might operate outside its safety envelope or under conditions close to the limit values defined by the envelope. In this context, each of the parameters taken into account by a control unit can vary within a range defined by threshold values. Each of the threshold values is defined by taking account of the maximum threshold values for the other parameters. For example, the maximum allowable cant value for the ground on which the elevating platform stands is determined by taking account of the maximum height and of the maximum offset of the platform relative to the ground, and/or of the maximum weight of a load disposed on said platform and/or of the maximum speed of the wind to which the elevating platform can be subjected.
However, it is sometimes necessary for an elevating platform to operate under conditions that lie outside the normal operating range, which is not possible with current elevating platforms, without endangering the user and anyone in the vicinity of the elevating platform.